A level is an instrument used by carpenters, masons, surveyors, builders and the like to tell when a surface is level or horizontal to the earth or to tell more particularly when a measuring device is appropriately aligned to take horizontal or vertical measurements.
One of the most accurate levels which has been employed is called the spirit level which is simply a glass tube filled with a liquid and containing a bubble of air. The center of the tube may be slightly curved so that when the level is held horizontal the center is the highest point to which the bubble rises in order to indicate an appropriate horizontal attitude.
One of the most important tools used by surveyors is known as a transit. This involves the use of a small telescope set up on a tripod and to which are attached horizontal and vertical measuring instruments adapted for the measurements of horizontal and vertical angles. The tripod and the telescope may be related to the horizontal by the aid of attached spirit levels such as mentioned hereinabove. A weight hanging down from the tripode may indicate the exact spot where the surveying instrument is set up.
There has been many patents directed to the above-indicated types of tools. For example, C. Larsen, in U.S. Pat. No. 918,869 discloses a clinometer comprising a graduated rod with a level and a tape line casing slidable thereon. A tape line is provided in the casing and a plumb bob is secured upon the end of the tape line. Readings taken from the rod and tape line will furnish the general inclination or slope of the ground between two spaced points.
Lester Pippin in U.S. Pat. No. 2,627,115 relates to instruments used by surveyors for measuring the height of a grade or sloping surface or fill wherein a vertically positioned measuring stick extends through a horizontally disposed bar having a spirit level therein wherein with the stick standing on a grade and the bar held in a level position with one end on the grade and the other on the stick the height of that point is indicated on the stick. Pippin indicates that in measuring elevations it is difficult to measure the height of the soil of ground without a surveyor's leveling instrument. Moreover, he states that in numerous instances particularly in making fills for roadways and in grading fields on farms and the like it is desirable to ascertain the depth without the necessity of resorting to surveyor's instruments. With this in mind the invention was directed to a device including a pair of telescoping rods or sticks with a spirit level in one member and with units of measure indicated on the other whereby with the member on which the units of measure are provided held in a vertical position and the member with the spirit level held horizontal the depth of a sloping surface may be readily determined.
Sherman Calver in U.S. Pat. No. 2,753,633 provides an improved slope gauge device for establishing grades either in cut or fill in earth-work operations, the device being adapted to enable a combination of different slope angles to be set up in a rapid and simple manner. The Calver apparatus is a slope gauge which comprises a calibrated vertical arm formed with apertures spaced along its length, a calibrated horizontal arm formed with apertures spaced along its length, both extending through and pivotally connecting the horizontal arm to the vertical arm at selected of the apertures, an inclined strut bar formed along its length with spaced apertures and bolts extending through selected apertures of the strut bar and apertures in the arms, there being furthermore provided a clamp detachably secured to one of the arms for engaging a stake, and a bubble level mounted on the horizontal arm.
Ray Bernard in U.S. Pat. No. 4,067,117 discloses a spirit level having a measuring stick slidably mounted on one end of the level with means attached to the level for clamping and releasing the free transverse movement of the measuring stick from a position near the center of the level. A separate bracket is provided for attachment to the level for the clamping device which bracket also includes a guide for the measuring stick. The clamping device includes a spring urged frictional brake which engages the measuring stick and is releasable by a thumb operated handle slidably mounted adjacent a vial which indicates when the level is horizontal. The guiding bracket may be longitudinally extended with respect to the level to increase the length thereof.
William Eitzen in U.S. Pat. No. 2,746,164 disloses an invention which relates to carpenters' or builders' levels and has the object of providing a readily attachable or removable grade or slope measuring device on one end of a level so that the grade may be immediately read in desired linear units. In this apparatus a rule can be locked in downwardly extended position relative to a level by movement imparted by a pinion. Knowing the length of the level, an operator can read the grade of the slope from the rule by noting the linear distance shown by an indicator in linear units.
Boyd Barbee in U.S. Pat. No. 3,335,498 discloses an invention which relates to a carpenter's measuring tool of the type to be utilized to perform a variety of functions. The object of the Barbee invention is to provide a carpenter's measuring tool of T-square configuration in which the shank is movable along the crossbar to increase the effective length of the crossbar such that a perpendicular longer than half the length of the crossbar may be drawn.
James Webb in U.S. Pat. No. 2,807,887 provides in combination with a flexible measuring tape having scaled indicia on one face thereof a level indicating device which comprises a body including a plate having a ledge transversely across one face and intermediate the ends thereof to provide a support for one edge of the tape. Further a clamp carried by the body releasably secures the level indicating device on the tape at a selected location therealong, a weighted level indicator carried by the body for free movement is an arcuate path about an axis adjacent one end of the body and perpendicular to the longitudinal axis of the tape being moreover provided. The indicator includes a free pointed end defining an indexing pointer arranged below and adjacent said ledge to cooperate with the scaled indicia on the tape to show any deviation of the tape from a horizontally extending position.
Joseph Caruso in U.S. Pat. No. 2,942,348 shows a combination tape case and leveling device in which a coiled measuring tape is housed in a casing in which is installed a leveling device.
Alphonse Rodriguez in U.S. Pat. No. 1,400,626 and Oswin Moll in U.S. Pat. No. 3,242,578 show additional devices involving features which are employed in the present invention. Specific reference is made to U.S. Pat. No. 3,242,578 in which two level devices arranged at right angles to each other are employed.
All the above devices show many of the features collectively involved in constructing an apparatus in accordance with the present invention. However, none of the prior art patents show all of the features nor the advantageous results obtained in combining the various features in a single operative apparatus suitable for determining grades and making other related measurements.